Bushings



F. J. COREY Sept. 10, 1957 'BUSHINGS Filed April 5, 1953 FIG. 2

I lNVENTO/ FRANK J. c REY NEY United States Patent BUSHINGS Frank J. Corey, Belmont, Mass., assignor to Raytheon Manufacturing Company, Newton, Mass, :1 corporation of Delaware Application April 3, 1953, Serial No. 346,636 Claims. (Cl. 174-153) This invention pertains to a hermetically-sealed insulating bushing for bringing out an electrical conductor from the wall of an enclosed electrical device.

It is desirable in hermetically-sealed electrical devices to obtain a lead-in bushing which will not loosen because of expansion or contraction of the conductive member and the surrounding insulator body, and which will prevent leakage from occurring between the bushing and the surrounding wall. Another requisite of a satisfactory bushing is that the insulator body be sufficiently plastic so that it will not break or loosen when the device is subjected to shock and vibration. The bushing should be also capable of maintaining a hermetic seal in spite of the presence of moisture and corrosive materials in the vicinity of the device. Finally, the bushing must have good insulating properties to prevent electrical breakdown or corona between the conducting member and the wall of the device.

Glass bead terminals have been used in hermeticallysealed electrical devices because a seal may be easily obtained, by usual vacuum tube techniques, between the lead-in conductor and glass and between the glass and the metal ring serving as a means of soldering the terminal to the case. Such terminals, however, are mechanically deficient inasmuch as glass will not withstand rough handling incident to production, vibration imparted from associated equipment, shock caused by rapid temperature cycling, or the effect of high humidity when a polarizing voltage is applied.

In accordance with this invention, an apertured plastic insulator body is inserted by a slight pressure within an opening in a supporting wall whose diameter is slightly smaller than the outer diameter of the insulator body. A flange forming an integral part of the insulator is adapted to rest against the under surface of said wall. A conductor having two spaced enlarged portions of a larger size than the normal unexpanded size of the aperture in said insulator is forcibly driven into and through said insulator body so that the enlarged portions of the con ductor are on the opposite side of the mounting wall from the insulator flange. The insulator body, therefore, is expanded on the opposite side of the wall from said flange until an interference fit is obtained between the outside of said insulator body and the wall, as well as between the conductor and said insulator body.

The conductor may have a threaded end opposite the driven end for receiving a nut which may be tightened up against the flange portion of the insulator to decrease the likelihood of withdrawal of the conductor from the insulator with either temperature changes or vibration. Alternatively, the end of the conductor opposite the driven end may be drilled out to leave a thin wall portion. This lower end is adapted to fit over a spring-loaded pin of a rigid supporting anvil. An apertured lug is inserted over the anvil pin with the aperture aligned with the lower end of the conductor and the anvil, including the lug, is positioned in contact with the bottom surface of the insulator flange. When the conductor is driven through 2,806,080 Patented Sept. 10, 1957 ice the insulator lug and against the anvil, the thin walls at the end of the conductor are upset against the bottom surface of the lug. In this way, the lug is securely fastened to the conductor and the tendency for the conductor to loosen or pull out is reduced, just as in the case of the threaded conductor.

To further improve the seal, a driving tool, which is inserted over the end of the conductor opposite the thin walled end, is to shaped that, when force is applied to the tool causing it to move downward toward the supporting wall, some of the plastic material of the insulator body is forced into a shoulder recess in the conductor formed between the two spaced enlarged portions thereof.

To make the bushing assembly practically non-turning, the periphery of one of the enlarged portions of the conductor is serrated so as to firmly lock the conductor into the plastic insulator.

Fig. 1 is an exploded view of the constituent parts of a first embodiment of an insulating bushing, according to the subject invention, including a device necessary for assembling said parts;

Fig. 2 is a central longitudinal cross-sectional view of the assembled bushing of Fig. l; and

Fig. 3 is a cross-sectional view of a modification of the bushing shown in Figs. 1 and 2.

Referring to Figs. 1 and 2 of the drawing, a bushing 10 is shown consisting of an irregularly shaped conductor 11 and an insulator body 12. Conductor 11 is made, preferably, of an easily machinable metal of reasonably high electrical conductivity, such as hard yellow brass. Conductor 11 is provided with a number of regions of difierent diameters and configurations. At one end of the conductor is a terminal lug 14 whose diameter is approximately equal to that of bore 13 in insulator body 12. Lug 14 includes a head portion 15 of slightly larger diameter. Lead wires, not shown, may be attached to said terminal lug as by soldering. Adjoining terminal lug 14 is a first enlarged portion or shoulder 16, whose maximum diameter is considerably larger than that of bore 13. Shoulder 16 has a tapered portion 17 terminating in a reduced region 18, which may be of the same size as terminal lug 14. Region 18 leads into a second enlarged portion or shoulder 20 having oppositely tapered sections 19 and 21. The lower tapered section 21 facilitates entrance of the conductor into the insulator body. A shoulder recess 22 is formed by the reduced region 18 and the tapered portions 17 and 19 of shoulders 16 and 20, respectively. Finally, a reduced cylindrical stem 24 is drilled and countersunk, as at 25, to form a thin walled end extension, as shown clearly in Fig. l. The diameter of stem 24 may be the same as that of terminal lug 14 and region 18. The drilled hole 25 is such as to leave a thin walled extension which may be readily upset while possessing the necessary mechanical strength. In one example, this wall portion 26 of conductor 11 was about long and about & thick; the values given, of course, are merely illustrative.

Insulator body 12 is made of resilient material having high resistivity and considerable plastic memory. The latter may be defined as the ability of the material eventually to recover its original shape after removal of a deforming load. In practice, it has been found that fluorocarbon resins such as polytetrailuoroethylene (otherwise known under the trade name Tefion) are quite satisfactory. Electrically, these fluorocarbons are characterized by a volume resistivity well over 10 ohm-cm, high dielectric strength in the absence of corona, and excellent arc resistance. Moreover, polytetrafluoroethylene is chemically inert, does not absorb moisture, and has a high heat resistance. Other materials such as nylon may be used with varying degrees of success.

Insulator body 12 has a substantially cylindrical neck hole 30 from the opposite side of the wall 28 from 32 which is slightly tapered, as shown in Fig. 1, for reasons to be pointed out subsequently. Insulator body 12 also includes an integral shoulder portion or flange 34. A cylindrical bore 13 extends longitudinally, through the insulator. t I

'Bushing is adaptedto be inserted through a wall 28 which may be, for example, the top of a transformer housing. Wall 23 has an extruded mounting hole 30, which, although shown as circular, may be of any do sired shape, such as rectangular or oval. The extrusion results in a neck portion 28' of wall 28 being upset, as shown in Figs. 1 and 2. -While the mounting hole may be formed by an extrusion process, the wall may be drilled if the wall material is sufliciently thick.

The diameter of insulator neck 32, at its junction with flange 34, is slightly larger than the diameter of mounting hole 3% in. wall 28, so that the insulator will have an interfering fit with the hole 30. The minimum outer diameter of the insulator is slightly smaller than that of hole 30 to facilitate insertion of the insulator into the hole. It mounting hole 30 is other than circular, the contour of the shank 32 is made to conform to said hole.

The bushing may be assembled by inserting insulator body 12 into a hole 34 in wall 28 so that the flange 34 engages a portion of the underside of the wall, as shown in Fig. 2. This may be done by hand since relatively little pressure is required.

A connecting lug 36 is inserted over pin 38 of a conventional spring-loaded rigid anvil 40. Lug 36 has an opening 37 which is slightly larger than the outside diameter of the thin walled portion 26 of conductor 11. The anvil 4t carrying lug 36 is positioned against the bottom surface of insulator flange 34 with the anvil pin 38 extendin" upward through a portion of insulator bore 13. The workpiece 42 of anvil 40 contains an annular groove or recess 43 for reasons to be stated later. The stem 24 of conductor 11 is next inserted in mounting that occupied by flange 34.

A recessed driving tool 45 is inserted over the upper end of conductor 11. This tool contains a first recessed portion 47 of approximately the same dimensions as head of conductor 11, and is adapted to receive said head. Recessed portion -37 flares in to a larger recessed portion 43 which is made sufficiently large to clear the upper shoulder 16 of conductor 11. The recess is finally tapered, as shown at 49, to form a shoulder 50 on the inside of the driving tool.

A large force is applied to the top of the driving tool and the conductor is thus driven into and through the plastic insulator 11 and lug as against the surface 42 of anvil 40. The combined action of the thin walled end of conductor ll striking anvil surface 42, and of the pin entering counter bore 26, upsets wall 26 against lug 36, as shown in Fig. 2, thus firmly attaching the lug to the bushing. Electrical connections, such as lead wires, may be attached to the lug by soldering or any other desirable means. The grooved portion 43 of anvil surface 42 is adapted to receive the upset portion of conductor 11.

The plastic insulator body is deformed by the entrance under pressure of the enlarged shoulder portions 16 and 20. These portions are tapered to facilitate entrance into insulator bore 13. Shoulder 16 of conductor 11, which comes to rest above the upper surface of wall 28, forces the insulator outwardly in the region 52 just above the extruded wall until its diameter is in excess of that of mounting hole 3%) in the wall; The expansion of the insulator body causes an outward pressure to be exerted on the interior surfaces of the upset portion 28' of the wall. In this manner, movement of insulator 11 in mounting hole 31) is prevented and a hermetic seal between the insulator and mounting wall is provided.

The shoulder portion 50 of the driving tool, when 4 driven downward, forces the plastic material of the insulator into the recess 22 formed between the two enlarged portions or shoulders 16 and 20 of conductor 11.

The periphery of shoulder 20 is serrated so that the edges sink into the plastic material of the insulator, thereby preventing rotation of the conductor.

Because of the plastic memory of the material of which the insulator is made, it tends to return to its original shape after the deforming force is removed. Since the diameter of conductor 11 exceeds that of bore 13, a very tight seal is also formed between the conductor and the innermost portion of the insulator.

In Fig. 3, a modification of the bushing of Figs. 1 and 2 is shown in which the stem 24 is threaded to accommodate a nut 55, lug 36, and washer 56. When the nut is tightened, lug 36 is securely attached to the insulator and any tendency for the conductor to back out is lessened. The anvil used in forming the bushing of Fig. 3 need not be spring-loaded and need not contain a groove or recess in the work surface, as in the case of the anvil shown in Figs. 1 and 2. This is true because the conductor stem need not be upset and no allowances need be made for expansion of the upset wall. The anvil used in the bushing in Fig. 3 need only have an aperture larger than that of the stem portion of the conductor.

This invention is not limited to the particular details of construction, materials and processes described, as many equivalents will suggest themselves to those skilled in the art. It is, accordingly, desired that the appended claims be given a broad interpretation commensurate with the scope of the invention within the art.

What is claimed is:

l. A bushing comprising a mounting wall having upper and lower surfaces and having an aperture therein, a resilient insulator body having the property of plastic memory, said insulator body including a flange portion adapted to engage the lower surface of said wall and a neck portion extending upward through said aperture, said insulator body further containing a longitudinal bore, an electrically-conductive member extending through said bore and including upper and lower portions of substantially the same size as said bore and an intermediate portion substantially larger than said bore, said lower portion including a thin walled extension, said intermediate portion of said conductive member causing expansion of said neck of said insulator body in the region adjacent to said aperture and on the side of said wall opposite said flange by the insertion of said conductive member through said bore, said intermediate portion of said conductive member being serrated to prevent rotation of said conductive member, and retaining means on said conductive member disposed adjacent to said flange portion of said insulator body and formed by upsetting of said thin walled extension.

2. A bushing as recited in claim 1 in which said insulator body is composed of a fluorocarbon resin.

3. A bushing comprising a mounting wall having upper and lower surfaces and having an aperture therein, a resilient insulator body having the property of plastic memory, said insulator body including a flange portion adapted to engage the lower surface'of said wall and a neck portion extending upward through said aperture and forming an interference fit therein, said insulator body further containing a longitudinal bore, an electrically-conductive member extending through said bore and including upper and lower portions of substantially the same size as said bore and an intermediate portion substantially larger than said bore, said intermediate portion of said conductive member causing expansion of said neck of said insualtor body in the region adjacent to said aperture and on the side of said wall opposite said flange by the insertion of said conductive member through said bore, said intermediate portion of said conductive member being serrated to prevent rotation of said conductive member, a connecting lug positioned beneath said flange portion of said insulator and surrounding said lower portion of said conductive member, and retaining means on said conductive member in contact with said connecting lug and having a diameter greater than that of said bore.

4. A bushing comprising a mounting wall having upper and lower surfaces and having an aperture therein, a resilient insulator body having the property of plastic memory, said insulator body including a flange portion adapted to engage the lower surface of said wall and a neck portion extending upward through said aperture, said insulator body further containing :a longitudinal bore, and an electrically-conductive member extending through said bore and including a head portion, spaced first and second enlarged portions, each substantially larger than said bore, and a stem portion, in that order, said neck portion of said insulator body including an outwardly expanded portion whose diameter is greater than that of said aperture and located adjacent said aperture on the side of said wall opposite said flange, said neck portion of said insulator body further including a portion disposed within the region between said tirst and second enlarged portions of said conductive member.

5. A bushing as recited in claim 4 in which said insulator body is composed of a fluorocarbon resin.

*6. A bushing comprising a mounting wall having upper and lower surf-aces and having an aperture therein, a resilient insulator body having the property of plastic memory, said insulator body including a flange portion adapted to engage the lower surface of said wall and a neck portion extending upward through said aperture, said insulator body further containing a longitudinal bore, an electrically-conductive member extending through said bore and including a head portion, spaced first and second enlarged portions, each substantially larger than said bore, and a stem portion in that order, and an apertured connecting lug positioned beneath said flange and having its aperture aligned with said stem portion of said conductive member, said neck portion of said insulator body including an outwardly expanded portion whose diameter is greater than that of said aperture and located adjacent said aperture on the side of said wall opposite said flange, said neck portion of said insulator body further including a portion disposed within the region between said first and second enlarged portions of said conductive member, said second enlarged portion being serrated to pre vent rotation of said conductive member.

7. A bushing comprising a resilient insulator body having the property of plastic memory and including an enlarged flanged portion at one end thereof, said insulator body containing a longitudinal bore, an electrically-conductive member extending through said bore and including first and second end portions of substantially the same size as said bore, two spaced intermediate portions each substantially larger than said bore and forming therebetween a recess of reduced cross section, said insulator body including an outwardly expanded portion of enlarged cross section in the region adjacent one of said intermediate portions, said insulator body further including at the other end thereof a portion disposed within the recess between said two intermediate portions.

8. A bushing comprising a resilient insulator body having the property of plastic memory, said insulator body containing a longitudinal bore, an electrically-conductive member extending through said bore and including first and second end portion of substantially the same size as said bore, two spaced intermediate portions each substantially larger than said bore and forming therebetween a recess of reduced cross section, said insulator body including an outwardly expanded portion of enlarged cross section in the region adjacent one of said intermediate portions, said insulator body further including a portion disposed within the recess between said two intermediate portions, said one intermediate portion being serrated to prevent rotation of said conductive member.

9. A bushing comprising a resilient insulator body having the property of plastic memory, said insulator body containing a longitudinal bore, an electrically-conductive member extending through said bore and including first and second end portions of substantially the same size as said bore, two spaced intermediate portions each substantially larger than said bore and forming therebetween a recess of reduced cross section, said insulator body including an outwardly expanded portion of enlarged cross section in the region adjacent one of said intermediate portions, said insulator body further including a portion disposed within the recess between said two intermediate portions, and retaining means including an upset thinwalled extension on one of said end portions.

10. A bushing comprising a resilient insulator body having the property of plastic memory, said insulator body containing a longitudinal bore, an electrically-conductive member extending through said bore and including first and second end portions of substantially the same size as said bore, two spaced intermediate portions each substantially larger than said bore and forming therebetween a recess of reduced cross section, said insulator body including an outwardly expanded portion of enlarged cross section in the region adjacent one of said intermediate portions, said insulator body further including a portion disposed within the recess between said two intermediate portions, one of said end portions being threaded to receive a nut which may be tightened against a portion of said insulator body.

References Cited in the file of this patent UNITED STATES PATENTS 1,346,539 Gray July 13, 1920 2,245,918 Hobbs June 17, 1941 2,304,334 Boucher et al. Dec. 8, 1942 2,406,852 Relf Sept. 3, 1946 2,431,951 Mauerer Dec. 2, 1947 2,433,911 Johnston Jan. 6, 1948 2,443,545 Schwennesen June 15, 1948 2,592,130 Erb et al Apr. 8, 1952 FOREIGN PATENTS 641,917 Great Britain Aug. 23, 1950 

